Different Grade Designations for Sheet Metals

Blog | October 24th, 2018

There are, as the post title infers, different sheet metals grades. On the one hand, the abundant number of grade designations ensures a match will always be available for a specified application. With that said, a sheet metal fabricator needs to keep ahead of the curve. We need to know every designation and what it means to the machining operation, plus how it’ll affect a product after it’s installed.

Carbon Steel Sheeting and Its Alloying Elements 

Generally, the SAE (Society of Automotive Engineers) covers carbon steel and a range of low-alloy metals. The designations assigned to the various steel alloy families form into four-digit strings. The first number identifies the primary alloying element. The second number provides more data about the material. Pairing the last two numbers, these codifiers indicate carbon content percentile. Welders and machine operators tend to pay attention to those last two digits. Set high, they suggest a hard to weld and difficult to machine microstructure. Incidentally, that first digit, say it’s a 1xxx alloy, is part of the carbon steel family. Other numbers, including 2xxx and 9xxx, specify other alloying elements, including nickel, manganese, and silicon.

Aluminium Sheets: Determining Lightweight Grade Designations 

Yet again, the four-digit alloy designation system comes into effect. Only, this time around, the numerical identifiers have different meanings. Starting with the first digit, we read the alloying element. For example, 1xxx series aluminium is almost pure, but series 2xxx adds copper. The second number signals a process modification, while the last two digits are furnished as an arbitrary, series codifying identifier. Last of all, the H.T.O heat treatment and tempering identifiers are appended to the four-digit alloy designation. Letter ‘O’ stands for annealed, letter ‘H’ for Strain Hardened, and the letter ‘T’ is assigned when aluminium sheeting is Heat Treated.

Graded Stainless Steels 

Lopping one number from the string, iron-heavy, chromium-rich stainless steels opt for a three-digit grade designation system. Looking at a grade datasheet, we see that type 301 stainless steel is popular. That first number demonstrates the ferrous metal’s microstructure. The 3xx designator proves the steel has an austenitic form, which is extremely workable and machinable. 4xx stainless, on the other hand, exhibits a ferritic microstructure, which resists heat treatment. However, 400 series metals are corrosion resistant and inherently strong.

Ultimately, the different grade designations show the sheet’s iron or aluminium content. However, the numerical strings also demonstrate certain alloying elements are locked inside the sheets, which are chemically and thermally injected into the primary metal base. Knowing these designations, the grades and various series identifiers, a sheet metal fabricator knows just how workable and weldable a sourced alloy is, just by translating the meaning behind each digit.

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